Pool type cathode with means for accelerating arc formation



y 1950 I E LANY ETAL 2,501,434

B. P. 0 POOL TYPE CATHODE WITH MEANS FOR ACCELERATING ARC FORMATION Filed July l 4,-1948 2 Sheets-Sheet 1 I I I,

.- 1%!(11. Cape/and M y 1950 E LANY ETAL 2,507,434

B. P. D POOL TYPE CATHODE WITH MEANS FOR ACCELERATING ARC FORMATION I 2 Sheets-Sheet 2 FiledJuly 14, I948 In$77f0n 15. 1 66272501? Del 4;? Paw/Z. Q aZQ'YZ Patented May 9, 1950 UNITED STATES rArewr-qornce POOL TYPE CATHODE WITH MEANS FOR ACCELERATING ARC FORMATION 14 Claims.

J This invention relates to a cathode for mercury arcs and has for one object to provide a cold cathode electrical rectifier. In the particular form here shown it may be described as a mercury pool type, cold cathode.

It has for another object to provide a cathode of the type indicated in which the discharge is initiated easily and may be maintained simply in trouble free operation.

Another object is to provide a cold cathode means for stabilizing the arc and for facilitating the transition from initial glow to effective are.

Another object is to provide in a cold cathode means for securing arc operation at low temperatures and without the use of auxiliary starting devices.

It is recognized that mercury arcs have been extensively used. In such devices in the past, however, substantial and relatively expensive auxiliary equipment has been required for starting the arc, and this fact has tended to limit the use of such devices. In general it has been .considered that pool type cathodes are justified only in the case of large installations in which the cost and bulk are not prohibitive. However, the cost and bulk of such auxiliary equipment has made the use of pool type cold cathodes prohibitively expensive in connection with small tubes. It is, therefore, one of the objects of the present invention to provide a pool type cold cathode which eliminates the necessity of auxiliary equipment and which is suitable for small installations and which at the same time gives rapid arc initiation and satisfactory operation over.long periods. I Another object is to provide a cathode of the type-indicated which will not be damaged or put out of operation by overloads, whether they be instantaneous, as will often occur, or long continued. a

The cathodes of the present invention are illustrated in the drawings and described herein. Before describing the drawings, the general theory of operation and construction will be outlined. :Generally the cathode comprises a pool of mercury'within a glass tube or envelope, and means are provided in one form or another for limiting the area of the mercury pool which is exposed.

-- This may comprise a constriction in the wall of the tube or other envelope within which the arc occurs. By this-means the cathode pool area exposed to the discharge is limited to something less. than the total .area of the pool. With this i's-combined in the tube or envelope an auxiliary cathode which in general consists of a conductor .in the form of a solid or relatively large area.

Beatrice Pearson De Lany, Miami Beach, Flag-and Paul L. Copeland, Chicago, Ill.

2;. Application July 14, 1 4 l' r fi6- I (01.250-2'75) In another form the-device of this invention comprises a cathode pool of large area which is divided 'by a 'const'riction preferably slot shaped. This constrictionproduc'es' an inner area of the pool which is relatively small and an outer area which is relatively large. 'Relatively'small openings such as pinholes may be formed in the constricting tube or other member.

The device generally comprisesin all forms a tube or envelope formed of insulating material such as glass. Within this is'placed apool of mercury and constricting means are provided which are effective to limit the cathode pool are exposed to the discharge. By means of this construction an eiiective mercury arc is provided which operates satisfactorily without auxiliary the areaiof the pools.

It is unnecessary here to describe or explore the various theories concerning the exact mechanism or process for the extraction of electrons y from this spot. It is sufficient to state-that arcs 'are characterized by high current densities at the cathode and that devices made according to the present invention operate satisfactorily as arcs. A theory of operation of the devices of this invention isthat the discharge from the anode is channeled or directed and that the current density at the cathode is increased, even before the spot forins, by the channeling. Because the current density is'high at the cathode as a result .of channeling, the formation of a spot is facilitated. After the spot is formed a limitation of the effectivearea by this channeling tends to maintain the existence of the spot. By effective area is meant the effective area of the cathode I pool exposed through the opening in the restriction. This area is substantially the projection of that opening upon the exposed surface of the cathode pool. The luminous spot is developed and the arc initiated promptly and satisfactorily.

Generally it may be said that there is at present no complete agreement as to the theory of electron extraction in cathodes of the pool type. However, in the devices of this application, by condensing the discharge from the mercury pool by meansof a constriction, it hasbeen possible to facilitate the transitionfrom glow to are and in-hne'typigal case tgmaintaln a true arcwi'th a cathode spot or; a current as low as 25'milli-v ailmperes. I -V 4 "-ure;:6.

Like parts are throughout the specification and the =drawings.

An auxiliary metal cathode may be used in addition to the mercury pool cathode. This cathode may be in the form of a wire or a metallic cone or a metallic tube or, thimble. It may also comprise a metallic film on the wall of an insulating member, which insulating member accomplishes "the dnstriction above referred to.

Mercury has been spoken of above as a suitable metal for forming the cathode pool. Another suitable metal is cesium, which, is a metailiquid at room temperatures which- -emits electrons freely and which is used in cerrTaJihtS iis'of gas discharge tubes. Its char sma-see radiiatibnfii-ffers from that of mercury. A choice bet'w'n the two metals would involve a eonsideration of the relative cost of the metals snag ofthe tvpe of radiation desired or useful in the ain-dearest to which the cathode is to beapplied.

" "ti-"lb "-advanteiges inherent in "the st-Yucftr ic' curreht from themnodeto the cathode.

invention :is ilhistmted-=more oi less diag'fammatically :in the' aceompanying -drawings,

-- Eigu're*8-is-*asection--taken at imea-a-cf'rniginoicated by lllte characters Generally the cathode of this invention -is-em- -,bodied in a tube, bulb or other envelope which 4s+gastight and from whioh the air has-been re-v movedand into-which atgas r a vapor may have pbeeninserted. -A-metal-anod e which may be of }nickel,- tantalum or any; other suitable-anode -inaterial"-i s;positioned within the envelope, and

a. cathode -formed -of mercury \OILQGSLUIILJS also positioned 'withinthe'se nvelope; 'lhe anode and =cathodeareconneoted through the envelope to A restriotion of :somessort isspos it'ioned tween the anodeandthe cathode. Withthese gener'al -featiires in its arm -1a;

red sm l s el ope or tube 1 -b ..:o ie alile .,-.1m i i1 re s ee trough the qwall of the envelope and throughT'the pool of ism-"t s eers -A cone 5 -01." a rfitalum is positioned theenjvelope ar' 'd bove' th'e i mercury and .@e i id e eenes' asenpperfeaed ortrun- "kzted asat l. p p

se me tends into the envelopes ta full contact with the cathode pool 3. It'iiiay wardly and contacts the upper surface of the cathodepool 3.

Throughout'the specification when the cath- Ude pooPisTe'ferred to as *being formed of mercury, :it is to :be understood that this word is msed hot-exclusively, but is to include other meinstead otmercury.

terials which remain liquid at normal operating temperatures and thus to include also cesium.

ln all o i the several forms of the device shown the cathode pool might be formed of cesium in Figure 3 the envelope llfthe "anode A; the cathode pool 3 and thelea'd-in wireitai ef-as shown in Figure 2. A glass tube 12 "isQpos'itinned within the envelope and'its'ends malybe flared as shown. They mayalsobe straie htland unflared. .At its lower end the glass tub'e 'li is iastened .tothe wall of the envelope "Ijbutl one or more openings 13 are left in the-tubeifaim within the. pooi- 3 so "that the material "of, the

pool may circulate through such. openings. At

:ra'te'd .metallic member Tits upper end the tuloe |2 'isiclosed .byagsei iioi4. As "shown the-membervmay be of copper. if desired a smalltubularpor'tion 15 defines the perforation through "the copper member M. m p In the form of Figure 4 the envelope l.,;'the

" anode 2, the J pool 3; the l'eaddnwireia' Fantlthe tube T2 with its .cpenings .or. perforationslt are all 'thesain'e as shown in. Figure '3. The'fupper end of the tube is partially closed by'a metallic member "f6 which may be perforated, 'asat l I- 1. Secured'tothe metallic memb'enifi and"tlefpe'n'ding downwardly from it and into thefpool a":plural ity ofmtal-wiresf'fla. Thesemay be of tungsten or other suitable material.

As shown in Fleur-e5 the envelope 'i thecet'thode 2,v the pool 3 and the 'lead-in-wiredi are the sameas shown in several previous figures. A

glass tube 5 8 is positioned within the-envelope 'and's'ealed to it about its upper eugesr'asat-"ls. Thetube is constricted and fiattened*atitslower -en'dfias at '29, to form'a slot-like opening f ftl.

' as that o'i Fi'gure b, and

' "'diiie'rs' from that a portion awe-aster the inner -'-surfa'ce' of The form shown in Figure 6 is the-f sainetas that shown in Figure '5, with one'exception' "*The tube "f8, which is "fiattene'dfiis prowesswan a 'pli'irality of small holes 22, oi-the order offiin holes. These maybe arranged regulariy orfir- "the" flattened-tube we is'-providetl wane-amaze of tungstenorequivalent material.

The use and operation of theiinvention in any 'A "tube with the cathode or the presentmenstruction'is inserted in a-=systemwhere it'maytbe 'ot sired to use a cold cathode which will start readily without auxiliary mechanism and with low current at relatively low potentials.

With the tube embodying the present cathode installed in any such system, the anode 2 and the cathode pool 3 are connected to sources of current and when the potential is sufficiently high, a spot is formed within the uncovered area of the cathode pool. Usually this spot will be formed at a point within the projected area of the open space within the restriction. For example, it will be within the open space of the funnel 9 Figure 2.

I In the forms of Figures 5, 6 and '7 it will normally be within the open space formed by the flattened tube [8. In the form of Figure 6 it may also form outside this area through one or more of the pinholes 22. Generally a spot is formed, and almost immediately .a regular complete arc is developed, and the device 'is then in full useful operation, and :because of the constriction the arc remains stable and continues until the device is disconnected from the source of current, or the electromotive force falls below a critical value.

The pinholes 22 are eifective only at relatively high gas or vapor pressure, of the order of A millimeter to millimeters of mercury. When the pressure is such as to make the pinholes 22 effective, the discharge passes through one or another of the pinholes and continues to operate through the hole with high stability, the spot occurring where the discharge through the hole strikes the mercury. The streamer of the discharge remains concentrated rather than spread afterit passes through the pinhole.

We claim:

I. In combination, an airtight envelope tonne of insulating material and substantially free from air, a pool of metal which is in liquid form at room temperature in said envelope, said pool comprising a cathode member, and an anode positioned within said envelope and spaced away from said cathode, and electrical connections to said anode and said cathode, and means for concentrating the electron action of the anode upon a limited portion of the cathode pool area, said. means comprising a generally funnel-shaped member with a wide open top and'a restricted open bottom, said top extending in the direction of said anode, said funnel-shaped member being in contact with said envelope and being provided with conductive surface means. 1

2. In combination, an airtight envelope formed of insulating material and substantially free from air, a pool of metal which is in liquid form at room temperature in said envelope, said pool comprising a cathode member, and an anode positioned within said envelope and spaced away from said cathode, and electrical connections to said anode and said cathode, and means for concentrating the electron action of the anode upon a limited portion of the cathode pool area, said ..means comprising a generally funnel-shaped member with a wide open top and a restricted open bottom, said top extending in the direction {of said anode, said funnel-like member being formed of insulating material and sealed at its positioned within said envelope and spaced away from said cathode, and electrical connections to said anode and said cathode, and means for concentratingthe electron action of the anode upon a limited portion of the cathode pool area, said means comprising a generally funnel-shaped member with a wide open top and a restricted open bottom, said top extending in the direction of said anode, said funnel-like member being formed of insulating material and sealed at its upper end to said envelope, and metallic film positioned upon the inner surface of said funnel-like member. I

4. In combination, an airtight envelope formed of insulating material and substantially free from air, a pool of metal which is in liquid form at room temperature in said envelope, said pool comprising a cathode member, and an anode positioned within said envelope and spaced away from said cathode, and electrical connections to said anode and said cathode, and means for concentrating the electron action of the anode upon a limited portion of the cathode pool area, said means comprising a tubular member formed of insulating material positioned within said envelope and extending at one end into said pool, there being a metallic partition positioned across the free end of said tubular member, said metallic partition being perforated.

5. In combination, an airtight envelope formed of insulating material and substantially free from air, a pool of metal which is in liquid form at room temperature in said envelope, said pool comprising a cathode member, and an anode positioned within said envelope and spaced away from said cathode, and electrical connections to said anode and said cathode, and means for concentrating the electron action of the anode upon a limited portion of the cathode pool area, said means comprising a tubular member formed of insulating material positioned within said envelope and extending at one end into said pool, there being a metallic partition positioned across the free end of said tubular member, said metallic partition being perforated, said tube being flared at its upper and lower ends.

6. In combination, an airtight envelope formed of insulating material and substantially free from air, a pool of metal which is in liquid form at room temperature in said envelope, said pool comprising a cathode member, and an anode positioned within said envelope and spaced away from said cathode, and electrical connections to said anode and said cathode, and means for concentrating the electron action of the anode upon a limited portion of the cathode pool area, said means comprising a tubular member formed of insulating material positioned within said envelope and extending at one end into said pool, there being a metallic partition positioned across the free end of said tubular member, said metallic partition being perforated, and metallic wire-like members extending from said partition to said pool.

7. In combination, an airtight envelope formed of insulating material and substantially free from air, a pool of metal which is in liquid form at room temperature in said envelope, said pool comprising a cathode member, and an anode positioned within said envelope and spaced away from said cathode, and electrical connections to said anode and said cathode, and means for concentratingthe electron action of the anode upon a limited portion of the cathode pool area, said means comprising a] generally funnel-shaped member with a wide" open top and a restricted carca ses 17 open bottom; isaid top xtendingdnithe-direction of said anode, said funnel-dike member being iflattened at that z-portion which is in contact with ithe pool.

8; In-combinat-ion,anairtight envelope formed (oninsulatingimateriaband substantially free from all", a'ipcoi 'ofmetal which :is in :=liquid -form-at room temperature imsaid :envelope,said pooleomlprising a cathode member, and an anode positioned" within saidenvelope and spaced-"away irom -said cathode, and electrical connections to said anode and said cathode, andmeans-forconrcentrating Etheielectron -.action=ofthe-anode upon :a-.limited,portion of the -.cathode-pool area, said means comprising Ia generally. funnel-shaped .member with :awide open top :and a restricted =op'en bottom said-topsextendingin1 the direction =df s'aid ianode, saidiunnel-like member being flattenedmtthatportion which-is incontact-with thBe-DOOI and being ,provided with a metallic @film onntsiinneriaceI :9. In combination, anairtight'envelope formed ref-insulating material and substantially free from air, 3213001 of-metal which is in-liquidform at room :temperatureainssaid eenvelope, said pool nompris- :ing a cathodemembeniand an anode positioned within saidenvelope and spacedcaway from said cathode, and electrical connections-to said anode ahd-said cathode; and-means for concentrating the electron action of the anode upon a- :limited gportion of the cathodepool area said means com- .prising a 'generally funnel-shaped member-with awide open topand a restriotecliopen-bottom said top extendingiin the Y direction of i said anode,- said funnel-like imember rbeing .iflattened. at that :porticmwhich is incontact with the pool, (and a plurality -.ofrelatively uninute-sperforations .in said flattened memberadja-centthe surface of said-pool.

l0. =I-n combination, an airtight envelope :formedsof' insulating material and substantially :free from air,-a-pool of metal which is insliquid atorm at roomtemperaturelim said envelope, I said =poo1 comprising acathode -member, and an anode positioned within:saidenvelopeland spaced 'away fromsaid cathode, and electrical connections to said zanode andl said=cathode, and means .tor concentrating theielectron action of the anode upon ailimited portion -ofthe cathode pool area, .said means comprising-sagenerally-iunnel-shaped -member with a wide open top and a restricted openvbottom saiditopextending in the directionof said-anode, :said funnel-likemember :being vflattened at that portion which isl-inzcontact withthe pool and sealed; to :said envelope adjacent its .upperend.

11.:In combination, .an airtightenvelope -..formedof insulating :mater-ial andsubstantially freezfrom air, apool ofmetal which .is in liquid form -at room temperature insaid en'velope, said pool I comprising: a cathode member, and-an anode positioned within said envelope -:and spaced away from said cathode, and electrical connections to .said'anode-and saidacathoda andmeans for con- .centratingthe :electron action -of the -.anode' upon a a -lim'itedjportion .o'flthe cathode ,pool area, said uppen end to said envelope, i and-lsemi-oconductive :Jfllinpositioned =uponithe-z inner. .-'-surface --:of said ziumrel-likeimember.

.In combination,

zan, fl-alrtight envelop :13.:In combination, an airtight envelope fo'rmed of"insulatingmater1a1land substantially free :rrom 1 air, .a pool-vof metal Whichiis in liquid :form at :room temperature in said envelope-, ssaid p001 comprisinga cathode member, and anranode vpositioned'within -said envelopeand spaced :away from said-.cathode; and electricaliconnections to :said anode and said-cathode, and means {or-eon- 'centrating the electron -;acti0n of the anodexupon a limited portion ofthe cathode pool area-said concentrating means comprising agenerallysfunnel-like member sealed at .its' upperand larger portion to-theinteriorof said-envelope and penetrating at its lower and narrower portion oontinuously into the liquid pool and provided on 'its inner face with a conductive surface dn-contact with the pool.

114; :In combination, an airtight envelope formed of insulating material and substantially free from air, a pool of'metal which is :in liquid wformatro'om temperature in said envelope, said pool comprising a-cathode'memberLandau anode positioned within said envelope and'spaced-away "from said cathode, and electrical connections to "said anode "and said cathode, and 'means for con- "centra'tingthe electron action ofthe anode upon -a limited portion of the cathode :pool area;- said means comprising a tubular member formed-of insulating-material positioned within: said envelope and extending at one end into contact with the'metal of said POOL'OHB end-of said-tubular 'member being'se'aled to'the envelope .andthe oppositeend'of thetubular member-being provided "with a constricted opening in general; alignment "withthe electron path between the-anode and r cathode, and electrically conducting :means-dn contact-with the metal of said'pool surrounding and extending outwardly -of said constricted opening.

B. PEARSON-DELANY. PAUL-L. COPELAND REFERENCES SPEED The *following references are of record in -the 'fileo'f patent:

UNITED STATES PATENTS I Number Name Date -.1;126-,:l7'7 Schaefer -Feb. -2,-=19'15 11,178,542 Skaupy. Apr. l1, 1'9 '16 1,223,412.8- Schaefer Apr..2e,.191'7 1,246,470 Rose Nov. "131T 1917 1,285,947 Conrad e 'N0v.,26, T918 2,016,885 Braband 'Oct. 8119 35 2,438,668 "Koch et'al Mar; 30;i9'48 2,458,205 Rose Jan. 4, 1.949

FOREIGN PATENTS Number Country "Date 

